Of course, some people get involved in studies because they want to be a part of something bigger. The folks who volunteer to lie in bed for three months with their feet elevated slightly above their heads so that scientists can study the physiological effects of being in zero gravity tend to be passionate about space flight. They get paid about $5,000 a month, which isn't quite peanuts. But spending that much time off your feet causes significant muscle atrophy and bone loss, so participants must get checked six months after the study ends and again after a year.